There are generally four types of joints used in concrete flatwork (slabs and pavements): isolation joints, expansion joints, construction joints and contraction joints. Isolation joints are used to create a separation between the concrete flatwork panel and adjacent panels or other building components, such as walls, columns, trenches, man-holes, bollards, etc. Expansion joints are used in the same way as an isolation joint except that it contains a compressible material or void space sufficient to accommodate subsequent expansion of the concrete flatwork panel(s). Construction joints are used at the termination of a single slab placement and thus defines the joint between adjacent panels cast independently. Construction joints are generally formed with removable or leave in place forms, sawcut full depth, or slip formed (temporary forms used with low slump concrete mixtures). Contraction joints are used as means of allowing for the concrete contraction by providing a plane of weakness. Contraction joints are often induced cracks created with the use of a saw cut, crack inducer, or tooled notch in the surface of the concrete.
Each joint type has its drawbacks and problems. Isolation joints often do not provide for positive load transfer between adjacent panels and other building components. Expansion joints are wider than other joints and therefore more prone to both joint spalling, such as damage to the joint edges, from wheeled traffic or other objects crossing and impacting the joint, and the intrusion of liquids. The intrusion of liquids can cause numerous problems including the pumping of saturated subgrade materials and faulting of pavement panels in exterior pavements, and subgrades heaving due to frost in cold climates or areas where expansive soils are found. Construction joints can also be prone to joint spalling under traffic especially if sufficient load transfer is not provided to create sufficient joint stability. Contraction joints are prone to dominant joint activation where some joints open wider than others, leading to the loss of load transfer through aggregate interlock thus also increasing the likelihood of joint spalling There are additional issues as well.
All four joint types are generally filled or sealed after their construction in an attempt to either protect the joint from spalling under traffic or prevent the ingress of moisture, liquids, contaminants, or bacteria. Load transfer with joint stability is most often provided in any of these joints through the use of either dowels, which are generally steel bars that are round or square in section, or keyways, which are tongue and groove type joints which can be formed with removable or leave in place forms.
There are products on the market that provide improved joint performance. Concerning load transfer, plate dowels are described in U.S. Pat. Nos. 6,354,760 and 7,481,031, the disclosures of which are incorporated by reference in their entireties. Concerning joint sealing, an assembly designed to seal joints during the construction stage and not afterwards is described in Patent Co-operation Treaty document number PCT/AU2009/001376, the disclosure of which is incorporated by reference in its entirety.